pre-commit language: system Hooks

language: system runs the hook command as-is using whatever is on PATH, with no environment build.

system hooks are the simplest and the most fragile: pre-commit builds nothing, so the tool must already be installed on every machine and runner.

What it does

For language: system, pre-commit does not create any environment. It simply runs entry with the matched filenames on the existing PATH. This is fast but means dependency management is entirely your responsibility.

Common usage

.pre-commit-config.yaml

- repo: local
  hooks:
    - id: cargo-fmt
      name: cargo fmt
      entry: cargo fmt --
      language: system
      types: [rust]
      pass_filenames: false

Keys

Key	What it does
language: system	Run entry on the existing PATH, no env build
entry	Command to execute
pass_filenames	Append matched filenames to entry (default true)
types / files	Which files trigger the hook
require_serial	Run the hook once, not in parallel batches

In CI

Install the underlying tool in an earlier pipeline step, since pre-commit will not do it for you. For tools that operate on the whole project rather than a file list (cargo fmt, go vet), set pass_filenames: false. system hooks are the usual cause of "works on my machine, fails in CI" when the runner lacks the binary.

Common errors in CI

"[ERROR] Executable <cmd> not found" is the signature system-hook failure: the binary in entry is not installed on the runner. Install it first, or switch to a language pre-commit can provision. If entry runs but processes no files, check pass_filenames and the types/files filters.